Impact tool

ABSTRACT

An impact tool for use in a well bore. The impact tool provides a hammer action through reciprocal movement of a cam within a spring mechanism. In an embodiment a drill bit is included to provide an impact drilling tool which requires minimum weight on bit to operate. The impact tool can therefore be run on coiled tubing and wireline.

[0001] The present invention relates to impact tools used within oil andgas wells and in particular, though not exclusively, to an impactdrilling tool which requires little or no weighting or preloading tooperate within a bore hole.

[0002] Typical impact tools such as hammer or percussion tools requireto be weighted to ensure that the working surface, for instance, a drillbit is held against a rock formation at the bottom of a bore hole andthe tool is maintained in a closed working position. This combinationensures that impact from a hammer piston within the tool onto the drillbit is transferred into the rock formation to cause it to fracture andthe depth of the bore hole to be increased. Thus the hammering action isdirectly proportional to the pressure applied with the drill against therock formation.

[0003] Applying weight to the drill bit however has the disadvantagethat on impact a significant reactive force and torque is exerted backup the tool and also the drill string on which the tool is mounted.Extreme vibration can also be experienced. This combination of effectscan cause mechanical failure of a component on the drill stringresulting in overall operational failure of the entire downholeassembly.

[0004] It is therefore an object of the present invention to provide animpact tool for use in a bore hole which does not require to be weightedor preloaded to operate.

[0005] It is a further object of at least one embodiment of the presentinvention to provide an impact drilling tool for use in a bore holewhich does not require to be weighted or preloaded to operate.

[0006] Thus if minimal weight is applied to the drill bit the reactiveforce, torsional force and resultant vibration are minimised to theextent that they become insignificant. It is then possible to usecomposite coiled tubing or wire, which cannot be used with standardimpact drilling tools due to lack of mechanical ability in torsion, asthe drill string.

[0007] Thus, it is a further object of at least one embodiment of thepresent invention to provide an impact drilling tool which can beoperated downhole via lightweight tubing/composite pipe such ascomposite coiled tubing.

[0008] It is a still further object of at least one embodiment of thepresent invention to provide an impact drilling tool which can beoperated downhole via an electric line or wireline.

[0009] According to a first aspect of the present invention there isprovided an impact tool for use in a bore hole from a surface, theimpact drilling tool comprising:

[0010] a substantially cylindrical body having a longitudinal axis, theaxis being aligned co-axially with the bore hole;

[0011] a first end, perpendicular to the longitudinal axis, havingattachment means to attach the tool to a string for connection to thesurface;

[0012] a second end including a working sub, the working sub including asurface for contacting a portion of the bore hole; and

[0013] a hammer unit located between the first and second ends, thehammer unit providing a hammer action to the working sub via reciprocalmovement of a cam within a spring mechanism.

[0014] Preferably the working sub is a drill bit wherein the surfacecontacts with a formation to increase depth of the bore hole.Alternatively the working sub may be a cylindrical body, the hammeraction on the body thereby causing a vibratory action to the sub suchthat the tool may be used to assist in moving a string through a wellbore. This arrangement is advantageous in high step/high inclinationwells.

[0015] Preferably the spring mechanism comprises at least one firstspring to bias the working unit towards the cam. The use of a cam inconjunction with a spring, the spring keeping the tool ‘cocked’, toprovide the reciprocating or hammer motion of the working sub providesthe tool with a self hammer action, and thus no weight is required uponthe drill bit to operate the tool as in the prior art.

[0016] Preferably the spring mechanism comprises at least one secondspring located adjacent the cam to act with the cam in reciprocalmotion. Preferably the at least one second spring comprises a springcage, the spring cage being attached to the cam. The spring cageincluding one or more springs which compress when the cam moves towardsthe first end of the tool.

[0017] Preferably the tool includes a drive shaft. More preferably thedrive shaft is located on the longitudinal axis. The drive shaft mayprovide rotational drive means to the cam and the working sub. Morepreferably the tool includes one or more drive keys. Preferably firstdrive keys are located between the cam and the drive shaft to preventthe cam rotating independently of the drive shaft while permitting thecam to move longitudinally with respect to the drive shaft. Preferablysecond drive keys are located between the working sub and the driveshaft to prevent the working sub rotating independently of the driveshaft while permitting the working sub to move longitudinally withrespect to the drive shaft. Advantageously the each drive key comprisesa ball bearing located in a complimentary slot, the slot arrangedlongitudinally on the tool.

[0018] The working sub is disconnected from the hammer unit; that is itis keyed to prevent rotational movement. However, the working sub isfree to move longitudinally against the force of the one or moresprings. When the working sub is a drill bit, this arrangementfacilitates the bit to drill and cut effectively in the bore hole byvirtue of the minimum weight on bit. This is due to the fact that thebit will have room to cut the formation more effectively because ineffect the impacting surface or cutting face will be intermittently incontact with the formation thereby breaking the formation in apulverising fashion and then clearing it of cuttings and debris. Thiswould not be possible if the bit was an integral part of the hammerunit, as in the prior art impact drilling tools, because a moresignificant reactive force would be required to lift a section of thetool which in turn would require more weight on the bit.

[0019] Preferably the impact tool may further include drive means, thedrive means being used to rotate the drive shaft. By including a drivemeans on the tool, the tool can be operated on a work string whichcomprises coiled tubing or electric line/wireline. If there are no drivemeans within the tool, drive is provided via the surface by rotation ofthe work string.

[0020] Preferably the drive means is a positive displacement motor(PDM). The drive means may be operated by a change of fluid pressure inthe string. Additionally, the drive means may be steerable to direct thesurface of the working sub. When the working sub is a drill bit,directional drilling from wireline or coiled tubing is achievable withthe tool.

[0021] A PDM is most appropriate for operating the tool on coiledtubing. Advantageously the drive means is a downhole electric motor foroperating the tool on an electric line. Advantageously also the drivemeans is a downhole battery for operating the tool on a wireline.

[0022] Preferably the cam includes a cam groove extending continuouslyaround the circumference of the cam. The cam groove may provide a camprofile which includes one or more ‘V’ grooves. The cam profile thusprovides a number of strokes per revolution of the cam. Each stroke willrefer to each downward motion of the cam and provide one impacting orhammer action of the drill bit against the formation. Preferably the ‘V’grooves have rounded peaks and troughs providing an undulating profileon the cam surface. The cycle time/stroke may be adjusted by varying thespeed of rotation of the cam, which is in turn controlled by the drivemeans. The speed of rotation is not dependent on whether the stringitself is rotating.

[0023] Preferably one or more cam follower pins are located within thecam groove. The cam follower pins are preferably located on the innersurface of an outer housing of the tool. Thus as the cam rotates it isurged into a reciprocal motion as the pins follow the profile of the camgroove. Preferably the outer housing does not rotate. The outer housingmay be isolated from the drive shaft by bearings. Preferably thebearings are mounted in a bearing housing located between the cam andthe drive means.

[0024] Preferably also the tool includes lubrication means. Morepreferably the lubrication means comprises at least one channel locatedon the longitudinal axis, adjoining the first end of the tool to thesecond end of the tool.

[0025] Preferably fluid in the form of drilling mud is pumped throughthe channel and exits at ports on the impacting surface, to bothlubricate the impacting surface and push cuttings away from theimpacting surface and aid their return to the surface.

[0026] Additionally, the tool may include a bumper sub or slip joint.The bumper sub or slip joint comprises a telescopic joint mounted on thelongitudinal axis, The bumper sub/slip joint is used to ensure slack inthe string is maintained, so that no weight from the string may beapplied to the working sub. More preferably, the bumper sub/slip jointincludes a weight sensor. The weight sensor may provide a signal to thesurface to indicate the weight being applied to the working sub. Thiswill allow an operator to adjust the string accordingly to remove weighton the working sub. The bumper sub/slip joint may also absorb anyreciprocal forces after an impact.

[0027] Preferably the tool includes a shear disc sub. The shear disc subis mounted between the attachment means and the drive means. The sheardisc sub provides a safety release if an unsuitable pressuredifferential is established within the tool.

[0028] Advantageously, the tool further comprises a release joint. Therelease joint is preferably ball operated, as is known in the art. Therelease joint is preferably mounted adjacent to the attachment means.Thus, in the event of the working sub or tool sticking downhole, releaseof the release joint will disconnect the string from the tool and allowother means to be used to retrieve the tool.

[0029] According to a second aspect of the present invention, there isprovided a method of drilling a bore hole from a surface, the methodcomprising the steps:

[0030] (a) attaching an impact tool including a drill bit to a workstring;

[0031] (b) running the string into a bore hole;

[0032] (c) operating the impact tool to provide a hammer action to thedrill bit via a reciprocating cam within a spring mechanism; and

[0033] (d) impacting a surface of the drill bit upon a formation at abase of the bore hole.

[0034] Preferably the string is a lightweight type, such as a compositepipe. Alternatively; the string is a coiled tubing. Advantageously, thestring is an electric line or a wireline.

[0035] Preferably the impact tool is according to the first aspect.

[0036] The method may further include the step of pumping fluid throughthe impact tool, in order to lubricate the drill bit and assist inremoving drill cuttings.

[0037] Preferably also a number of impact strokes per minute of thedrill bit is set by the speed of rotation of the cam.

[0038] Preferably also the method includes the step of steering thedrill bit by drive means.

[0039] These and other aspects of the present invention will now bedescribed by way of example, with reference to the accompanying drawingsin which:

[0040]FIG. 1 is a schematic view of a impact tool in accordance with thepresent invention;

[0041]FIG. 2 is an exploded cross-sectional view of a part of the toolof FIG. 1 illustrating the hammer unit; and

[0042]FIG. 3 is a side view of the cam of FIG. 1.

[0043] Reference is first made to FIG. 1 of the drawings, whichillustrates an impact tool, generally indicated by reference numeral 10,in accordance with the present invention The impact tool 10 has acylindrical body 12 which includes a first end 14 and a second end 16.The ends 14 and 16 are at opposite positions on a longitudinal axis ofthe body 12.

[0044] Starting to the right of FIG. 1, at the first end 14 of theimpact 10, there is located a tubing connector 18. The tubing connector18 provides connection between the impact 10 and a work string 19.Adjacent to the tubing connector 18 is a ball operated release joint 20.The ball operated release joint 20 is as known in the art. The balloperated release joint 20 provides for release of the impact tool 10from the work string 19 in the event that the drill bit 22 or the tool10 itself has become stuck in the bore hole. Adjacent to the balloperated release joint 20 is a shear disc sub 24. The shear disc sub 24provides a safety release if an unsuitable pressure differential isestablished within the tool. The shear disc sub 24 is as is known in theart.

[0045] Next in line to the shear disc sub 24 is located a slip joint 26.The slip joint 26 comprises a telescopic section 28 through which afirst part 30 and a second part 32 of the slip joint 26 can movelongitudinally in relation to each other. The telescopic joint 28 mayalso include a weight sensor (not shown). The weight sensor can transmita signal to the surface to indicate the weight of the impact tool 10below the telescopic joint 28.

[0046] Below the slip joint 26 is a positive displacement motor 34.Although a positive displacement motor will be described here, it willbe understood by those skilled in the art that any downhole drive meanssuch as an electric motor or a battery could be used to provide downholepower to the tool.

[0047] The positive displacement motor 34 is driven by fluid pumped fromthe surface through the aforementioned components of the impact tool 10.Mounted below the positive displacement motor are the remaining sectionsof the impact tool 10, which will be described hereinafter withparticular reference to FIG. 2. The impact tool 10 terminates at asecond end 16, with a drill bit 22. The drill bit 22 could be replacedby a sub, however in the preferred embodiment the tool 10 includes adrill bit 22 to act as an impact drilling tool. The drill bit 22includes an impacting surface 36 which is used to strike or impact uponthe formation at the base of the bore hole being drilled. The impactingsurface 36 is made of a hard cutting material.

[0048] Reference is now made to FIG. 2 of the drawings, whichillustrates the hammer unit 33 and a bit mandrel 52 providing the hammerto the drill bit 22 of the impact tool 10 towards the second end 16 ofthe tool 10. Located on the longitudinal axis is a drive shaft 35. Thedrive shaft 35 is rotated by the motor 34. The hammer unit 33 has anouter housing 37 which is a tubular member providing an outer surface 39of the body 12 and an inner surface 41. A bearing house 38 isolates thehousing 37 from the drive shaft 35. The bearing housing 38 is as isknown in the art. Additionally roto-glyd rings 68A,B are mounted betweenthe shaft 35 and housings 37,38 to allow the shaft 35 to rotate freelywithin the housings.

[0049] Below the bearing housing 38 is located a cam 40. The cam 40 isalso illustrated in FIG. 3. The cam 40 is a cylindrical element havingupon its surface a continuous cam groove 42. The cam groove 42 has anelliptical profile which can be considered as a ‘V’ groove with twosloping edges. Sloping edge 46 is the down stroke and the sloping edgeon the reverse of the cam 40 (not shown) is the reverse stroke. It willbe appreciated that any number of strokes may be incorporated in thetool by increasing the number of ‘V’ grooves in the profile.

[0050] Into the cam groove 42 is located a cam follower pin 43. Thisembodiment only provides one pin, but it will be appreciated by those inthe art that more than one pin may provide greater stability to the tool10. The pin 43 is a protrusion on the inner surface 41 of the housing39. The pin 43 locates within the cam groove 42 to provide a smoothsliding action continuously around the cam profile, as the cam 40 isrotated. Additionally as the cam 40 is rotated and the pin 43 isstationary the cam 40 will be forced to move in a longitudinal pattern,or reciprocating action, in relation to the pin 43 as the pin 43 travelsin the groove 42.

[0051] Adjoining the cam 40 is a spring cage 56. The spring cage 56provides cage springs 58 mounted longitudinally to provide a biasagainst which the cam 40 compresses when the cam 40 is forced upwards bythe action of the pin 43 in the groove 42. The impact stroke of the toolis aided by the extension of the cage springs 58 under the downwardmotion of the cam 40 by the action of the pin 43 in the groove 42.

[0052] On the inner surface 54 of the cam 40 are located two slots 48.The slots 48 are positioned longitudinally and have rounded edges.Complimentary slots 44 are located on the drive shaft 35. Positionedwithin the slots 44,48 is a ball bearing 50 providing a drive keybetween the cam 40 and the drive shaft 35. This arrangement locks thecam 40 to the drive shaft 35 so that the cam 40 rotates with the driveshaft 35 while allowing the cam 40 to move longitudinally.

[0053] This arrangement of drive keys also keys the bit mandrel 52 tothe drive shaft 35 to provide rotational movement to the drill bit 32while allowing the drill bit 32 to reciprocate in response to actionfrom the cam 40 and springs 58.

[0054] A shock spring 60 is located towards the second end 16 of thetool 10. The shock spring 60 is mounted between the shaft 35 and the bitmandrel 52. A nut 62 retains the spring 60 in an enclosure between theshaft 35 and bit mandrel 52. The shock spring 60 ‘cocks’ the tool and inconjunction with the cam ensures that the drill bit 22 reciprocates eventhough no weight from the drill string has been slacked down onto thedrill bit 22.

[0055] A central bore 62 through the body 12 of the tool 10 provides achannel for the flow of fluid from the surface to the impacting surface36 of drill bit 22. Returning to FIG. 1, it is seen that the bore 62 maysplay within the drill bit 22 to provide a multitude of radial ports 64on the impacting surface 36.

[0056] In use, impact tool 10 is mounted on a string 19 using aconnector 18. The string 19 as shown in FIG. 1 is coiled tubing. It willbe appreciated by those in the art that string 19 could equally be astandard drill string, composite pipe, electric line or a wireline. Inthe embodiment using a electric line or wireline, fluid flow will not beprovided from the surface.

[0057] Impact tool 10 is then lowered into a bore hole, the string maybe rotated or reciprocated as it enters the bore hole. When theimpacting surface 36 reaches the base of the bore hole or any removableobstruction (for example, scale precipitate) the drive mechanism 34 isactivated in order to rotate the drive shaft 35. The cam 40 rotates withthe drive shaft 35 by virtue of the drive keys 50. As cam 40 rotates itwill be urged into a reciprocal motion as the pin 43 on the housing 39follows the groove 42 in the cam 40. Cam 40 moving upwards against thespring cage 56 provides the upstroke of the tool 10, conversely theimpact stroke is created by a downward motion of the cam 40, aided bythe springs 58. The impact stroke is not created by a vertical dropalone, there is also a radial component because the springs 58 movementback is not instantaneous. Drill bit 32 is biased against cam 40 via thebit mandrel 52 by shock spring 60. Shock spring 60 ‘cocks’ the tool 10and consequently the drill bit 32 follows the impact stroke of thehammer unit 33. Each stroke causes the surface 36 of the drill bit 22 tostrike the formation and break it up in a pulverising action. The speedof the strokes is dictated by the speed of revolution of the cam 40,which in turn is controlled by the motor 34.

[0058] In a further embodiment of the present invention the drill bit 22is replaced by a cylindrical sub, as shown in FIG. 2. When the tool 10is inserted in the well bore on a string, the hammer action is used tovibrate the tool in the well bore and therefore aid the passage of thestring through the well bore. This embodiment is particularly useful inhighly stepped or highly inclined wells where gravity cannot be used tomove the string through the well bore. It will be appreciated that thisembodiment could be used within tubulars mounted in a well bore such ascasing and liner.

[0059] The principal advantage of the present invention is that bydisconnecting the working unit from the hammer unit an impact tool isprovided with minimum weight on it. By the use of a cam and springmechanism to provide the reciprocating or hammer motion, the toolprovides a self hammer action, i.e., the tool powers both the downstroke and the upstroke. In particular when a drill bit is used as theworking unit, no weight is required upon the drill bit to operate thetool, as in the prior art.

[0060] A further advantage of the present invention is that the drivemeans may be contained within the tool itself. In this way the standarddrill pipe sections used to form the string can be dispensed with and analternative lightweight composite pipe, such as composite coil tubing orin fact a simple electric line/wireline can be used. Thus, the tool ofthe present invention is more versatile downhole than current impacttools. Additionally, as little or no weight is required upon to operatethe tool, reactive forces and torque are minimised, thereby facilitatingthe use of composite pipe or coiled tubing.

[0061] A further advantage of the present invention is that it providesan impact drilling tool which can drill and cut more effectively in thebore hole than standard tools by virtue of the minimum weight on bit.This is due to the fact that the bit will have room to cut the formationmore effectively because in effect the impacting surface or cutting facewill be intermittently in contact with the formation thereby breakingthe formation and then clearing it of cuttings and debris. This wouldnot be possible if the bit was an integral part of the hammer unit, asin the prior art impact drilling tools, because a more significantreactive force would be required to lift a section of the tool which inturn would require more weight on the bit.

[0062] A yet further advantage of the present invention is that itprovides an impact tool which does not require a return fluid flow pathto operate. Typically prior art hammer tools are hydraulically operated,thus requiring fluid to be pumped from the surface and the pressuredifferential created is used to generate the percussion action/force.The present invention is purely mechanical, is not affected by hydraulicor differential pressure and consequently a return flow path is notrequired.

[0063] Various modifications may be made to the present invention,without departing from the scope thereof. For example the cam surfacescould be reversed such that the rotation of the cam could be provided byan outer rotating body while the cam follower pin could be located at astationary position on the longitudinal axis.

We claim
 1. An impact tool for use in a bore hole from a surface, theimpact drilling tool comprising: a substantially cylindrical body havinga longitudinal axis, the axis being aligned co-axially with the borehole; a first end, perpendicular to the longitudinal axis, havingattachment means to attach the tool to a string for connection to thesurface; a second end including a working sub, the working sub includinga first surface for contacting a portion of the bore hole; and a hammerunit located between the first and second ends, the hammer unitproviding a hammer action to the working sub via reciprocal movement ofa cam within a spring mechanism.
 2. An impact tool as claimed in claim 1wherein the working sub is a drill bit and wherein the first surfacecontacts with a formation to increase depth of the bore hole.
 3. Animpact tool as claimed in claim 1 wherein the spring mechanism comprisesat least one first spring to bias the working unit towards the cam. 4.An impact tool as claimed in claim 1 wherein the spring mechanismcomprises at least one second spring located adjacent the cam to actwith the cam in reciprocal motion.
 5. An impact tool as claimed in claim1 wherein the tool further comprises a drive shaft located on thelongitudinal axis.
 6. An impact tool as claimed in claim 5 wherein thetool further includes at least one drive key located between the cam andthe drive shaft to prevent the cam rotating independently of the driveshaft while permitting the cam to move longitudinally with respect tothe drive shaft.
 7. An impact tool as claimed in claim 6 wherein thetool includes a second drive key located between the working sub and thedrive shaft to prevent the working sub rotating independently of thedrive shaft while permitting the working sub to move longitudinally withrespect to the drive shaft.
 8. An impact tool as claimed in claim 5wherein the tool includes drive means, the drive means being used torotate the drive shaft.
 9. An impact tool as claimed in claim 1 whereinthe cam includes a cam profile which determines number of strokes perrevolution of the cam and thereby the cycle/stroke rate of the hammerunit.
 10. An impact tool as claimed claim 1 wherein the tool includes atelescopic joint mounted on the longitudinal axis.
 11. An impact tool asclaimed in claim 1 wherein the tool includes a shear disc sub.
 12. Animpact tool as claimed claim 1 wherein the tool includes a releasejoint.
 13. A method of drilling a bore hole from a surface, the methodcomprising the steps: (a) attaching an impact tool including a drill bitto a work string; (b) running the string into a bore hole; (c) operatingthe impact tool to provide a hammer action to the drill bit via areciprocating cam within a spring mechanism; and (d) impacting a surfaceof the drill bit upon a formation at a base of the bore hole.
 14. Amethod as claimed in claim 13 wherein the work string is coiled tubing.15. A method as claimed in claim 13 wherein the work string is awireline.
 16. A method as claimed in claim 13 wherein the method furtherincludes the step of pumping fluid through the impact tool.
 17. A methodas claimed in claim 13 wherein a number of impact strokes per minute ofthe drill bit is set by the speed of rotation of the cam.
 18. A methodas claimed in claim 13 wherein the method further includes the step ofsteering the drill bit.